Systems and methods for x-ray computed tomography

ABSTRACT

A system and method for X-ray computed tomography includes a robotic arm that moves an X-ray emitter around a subject in a curvilinear path and an X-ray detector that captures 2-dimensional views while the subject is scanned. Movements of the emitter and detector are coordinated such that the position and angle of the emitter relative to the detector remains substantially constant during scanning. A processor uses computed tomography to reconstruct an image of the subject from the captured 2-dimensional views. The robotic arm varies the pitch of the X-ray emitter during the scan to enhance the spatial resolution of the reconstructed image. The processor generates a projection transformation matrix based on movement of the robotic arm for each captured 2-dimensional view that is applied during reconstruction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Non-Provisional Ser. No.16/460,936, filed Jul. 2, 2019, which claims the benefit of U.S.Provisional No. 62/693,382, filed Jul. 2, 2018, and also claims thebenefit of U.S. Provisional No. 62/716,160, filed Aug. 8, 2018, eachwhich is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The subject application generally relates to computed tomography and,more specifically, to systems and methods of reducing computedtomography artifacts, compensating for movement of a subject during acomputed tomography scan, and imaging core samples.

BACKGROUND

Computed tomography (CT) uses an X-ray source and a corresponding X-raydetector to scan an object from a number of different positions orangles. During CT reconstruction, a computing system performs dataprocessing algorithms on data from the X-ray detector from the scans toreconstruct a 3-dimensional representation of the scanned object.

Core drills extract cylindrical samples of sediment and rock from theground for analysis. By analyzing extracted core samples, companies canmake informed decisions about where to drill for oil, gas, or othersubstances. One method of analyzing core samples is to retain the coresamples in metal sleeves and attach high temperature, high pressurelines to the bottom and top of the metal sleeves to determine propertiesof the core samples such as capillary pressure, density, immiscibility,and so forth. Soaps, alcohols, or liquid CO₂ can be introduced todetermine how best to extract substances from the ground associated withthe core samples. Core samples are typically monitored over a period oftime, which can span days or weeks.

CT scanning of core samples allows for non-invasive and non-destructiveanalysis of the different layers of each core sample. During CTreconstruction, a computing system performs data processing algorithmson data from the X-ray detector from the scans to reconstruct a3-dimensional representation of the core sample.

However, accommodating core samples in traditional CT scanningapparatuses presents logistical challenges. Core samples are generallyvery heavy, making it difficult to move core samples into position forscanning by a traditional CT scanner. Moreover, cores are typicallymounted inside of a metal sleeve, often with a rubber liner which canallow the cores to move when repositioned. Further complicating movementof the core samples is accommodating the high temperature, high pressurelines that are typically present during testing.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will become better understood with regard to thefollowing description, appended claims, and accompanying drawings.

FIG. 1A depicts an example setup for performing cone beam scans.

FIG. 1B depicts rotating the cone beam scan of FIG. 1A in an arc togenerate a plurality of surfaces.

FIG. 1C depicts rotating the cone beam scan of FIG. 1A in a circle toproduce a set of surfaces.

FIG. 2 depicts a cross-section of a cone beam 3D image of a diskphantom.

FIG. 3 depicts an embodiment of a complex scanning motion of the presentdisclosure.

FIG. 4 illustrates an embodiment of a complex curvilinear path of anX-ray emitter and X-ray detector.

FIG. 5A depicts an embodiment of a two-arm robotic scanning system.

FIG. 5B depicts an embodiment of a single-arm robotic scanning system.

FIG. 6 depicts an X-ray intensity image of an object and fiducials.

FIG. 7 depicts a processed X-ray view of the object and fiducials ofFIG. 6.

FIG. 8 depicts a filtered X-ray for enhancing the fiducials of FIGS. 6and 7.

FIG. 9A depicts an embodiment of a two-arm CT core sample scanningsystem for a plurality of core samples.

FIG. 9B depicts an embodiment of a movable single-arm CT core samplescanning system for a plurality of core samples.

FIG. 10 depicts example robotic arm positions during a scan of a samplecore by a two-arm CT core sample scanning system.

FIG. 11 depicts the range of robotic arm positions around a sample coreduring a scan by a two-arm CT core sample scanning system.

FIG. 12 depicts the relative positions and orbital paths of the roboticarms around a sample core during a scan by a two arm CT core samplescanning system.

FIG. 13A depicts the position of a sample core during an initial scan bya CT core sample scanning system.

FIG. 13B depicts the position of the sample core during a subsequentscan by the CT core sample scanning system.

FIG. 14 depicts example operations of a CT core sample scanning system.

DETAILED DESCRIPTION

The systems and methods disclosed herein are described in detail by wayof examples and with reference to FIGS. 1 to 14. It will be appreciatedthat modifications to disclosed and described examples, arrangements,configurations, components, elements, apparatuses, devices methods,systems, etc. can suitably be made and may be desired for a specificapplication. In this disclosure, any identification of specifictechniques, arrangements, etc. are either related to a specific examplepresented or are merely a general description of such a technique,arrangement, etc. Identifications of specific details or examples arenot intended to be, and should not be, construed as mandatory orlimiting unless specifically designated as such.

Throughout this disclosure, references to components or modulesgenerally refer to items that logically can be grouped together toperform a function or group of related functions. Like referencenumerals are generally intended to refer to the same or similarcomponents. Components and modules can be implemented in software,hardware, or a combination of software and hardware. The term “software”is used expansively to include not only executable code, for examplemachine-executable or machine-interpretable instructions, but also datastructures, data stores and computing instructions stored in anysuitable electronic format, including firmware, and embedded software.It should be noted that although for clarity and to aid in understandingsome examples discussed herein might describe specific features orfunctions as part of a specific component or module, or as occurring ata specific layer of a computing device (for example, a hardware layer,operating system layer, or application layer), those features orfunctions may be implemented as part of a different component or moduleor operated at a different layer of a communication protocol stack.

The systems and methods disclosed herein describe improvements to thefield of computed tomography that are particularly applicable toscanning and imaging core samples. The systems and methods do not relyon a priori calibration of specific material types, core diameters orcore holders and are therefore adaptable to any range of computedtomography configurations for scanning and imaging core samples.However, the systems and methods presented are also adaptable to othersuitable computed tomography configurations outside of sampling andimaging core samples.

Referring now to FIG. 1A, a setup for an example cone beam scan 100 ispresented. The setup for the cone beam scan 100 includes an X-rayemitter 102 and an X-ray detector 104. X-rays 108 from the X-ray emitter102 pass through an object and are detected by the X-ray detector 104,represented here as an array of X-by-Y pixels. According to Radon'stheorem, a set of one-dimensional Fourier spectra correspond to thesurface 106 in a 3D cloud of values representing a Fourier transform ofthe scanned object. Referring also to FIG. 1B, the cone beam scan 100′is illustrated where the X-ray emitter 102′ and the X-ray detector 104′are rotated around the subject in an arc 110 to generate additionalsurfaces 106′. Each projection contributes to the Fourier spectrum.

Referring now also to FIG. 1C, the cone beam scan 100″ completes a fullrotation in a circle 112 about the scanned object to produce a set ofsurfaces 106″. However, this circular scan is non-optimal with respectto the accuracy of the calculated density map for the computed 3D CTimage. Even if the acquisition process is ideal (e.g., monochromaticspectrum, no scatter distortions, and the X-ray detector has ideallinear sensitivity) reconstruction methods can only produce aninsufficient approximation. After all projections have contributed tothe Fourier spectrum, there is an area 114 in the spectrum that is notdefined. This area 114 is shaped as two funnels located at the “northand south poles” of the spectrum respectively.

Referring also to FIG. 2, depicted is a cross-section of a cone beam 3Dimage 200 of a disk phantom, generated for example using a circular conebeam scan of FIGS. 1A-1C. As illustrated, there is an obviousdegradation of spatial resolution in the vertical direction. Theexistence of the area 114 illustrated in FIG. 1C and the cone beam 3Dimage 200 of FIG. 2 illustrates the need to compensate for this area 114using a suitable scanning technique or reconstruction approach or bothto address this area 114.

One such approach, known as the Felkamp approach, uses approximation.Other approaches include compensating for the effect of the area 114 byadditional motion of the X-ray emitter 102 and detector 104 along adifferent trajectory. However, no system is ideal. While making thecircular motion described above with respect to FIGS. 1B and 1C, themotion of either the X-ray emitter 102 or the X-ray detector 104 can becorrupted by vibration or sag, for example due to wear of components.Further, if the object moves during a scan the resulted 3D image 200 canbecome corrupted.

Cone beam X-ray devices are popular and have commercial applications innumerous industries including but not limited to healthcare, thepharmaceutical industry, non-destructive quality control and qualityanalysis (QA), forensics, and so forth. There are multiple methods forsystem geometry registration when scanning one type of a phantom oranother. Each method includes one or both of the following assumptionsor restrictions: (a) the phantom is predefined and the design, geometry,and configuration are known a priori with a high level of mechanicalprecision, and/or (b) the system motion is nearly perfectly circular andonly a few parameters describing or defining imperfections have to becalculated.

Additionally, there are numerous methods of object motion registrationfor further compensation, which can be separated into the generalcategories: (a) motion registration using techniques and equipment basedon non-X-ray equipment, (b) motion registration using special markers(typically high-density markers) which are visible on the X-rayprojections, and (c) motional registration based on internal samplestructure analysis (e.g., human anatomy). Some commercial motionregistration systems generate magnetic fields and use special sensors.Many commercial motion registration systems include motion capturesystems that are based on stereoscopic principles and which includemultiple high resolution video cameras working in the infra-redspectrum. However, multimedia approaches can be complex and expensive.Multimedia approaches require two separate tasks to be performed: (a)first the scanning system must be measured to determine how the scanningsystem moves in real-world X, Y, and Z coordinates, and (b) second,during an active phase of the scan, movement of the scanned object iscaptured by the video cameras or motion capture system. After the scan,these two geometry datasets are superimposed to produce the cone beam 3Dimage.

The CT reconstruction process of the present disclosure performs a scanthat compensates for the movement of the scanned object withoutrequiring a separate motion capture system. Assuming that the scannedobject is rigid, and using the <X,Y,Z> coordinate system, thecoordinates for any particular point of the scanned object do not changerelative to one another. The X-ray detector can be assumed to be flatwith its own local coordinate system <U,V>. For a system at a particulartime t, when an X-ray projection is captured, any point belonging to thescanned object with coordinates <X,Y,Z> will be associated with thecorresponding “shadow” on the detector plane with coordinates <U,V> ascalculated by the following formulas:

$U = \frac{{A_{00}*X} + {A_{01}*Y} + {A_{02}*Z} + {A_{03}*1.0}}{{A_{20}*X} + {A_{21}*Y} + {A_{22}*Z} + {A_{23}*1.0}}$$V = \frac{{A_{10}*X} + {A_{11}*Y} + {A_{12}*Z} + {A_{13}*1.0}}{{A_{20}*X} + {A_{21}*Y} + {A_{22}*Z} + {A_{23}*1.0}}$

where A₀₀ . . . A₂₃ are constants for this particular system position,and A₀₀ . . . A₂₃ can be defined as projection transformation matrix A.Thus for making a CT reconstruction when a scanning system and a scannedobject make a motion of any type of complexity, it is sufficient toobtain X-ray 2-dimensional set of views plus projection transformationmatrices A, with one matrix for every system position (every input2-dimensional view.) Therefore collecting data about system motion andobject motion can be performed using a single process, instead of twodifferent processes that require applying two different techniques asdescribed for the multimedia approaches.

Referring now to FIG. 3, an embodiment of a complex scanning motion 300is presented. The complex scanning motion 300 can be most easilydescribed using aviation terminology to describe the movement of theX-ray emitter 102 and X-ray detector 104. Assume that the X-ray emitter102 represents an aircraft cockpit while the X-ray detector 104represents the aircraft tail. The X-ray emitter 102 and X-ray detector104 are fixed relative to one another and move in tandem. While theX-ray emitter 102 and X-ray detector 104 rotate about 180 degrees ormore of “yaw”, the X-ray emitter 102 and X-ray detector 104 also make asmooth sinusoidal “pitch” wobbling within a few degrees, for example5-10 degrees. As illustrated in FIG. 3, the scanned object 302 is viewedfrom the side as the X-ray emitter 102 and X-ray detector 104 movethrough 180 degrees of yaw, and the X-ray emitter 102 and X-ray detector104 wobble in a sinusoidal motion from a maximum of about 5 degrees whenyaw is at 45 degrees to a minimum of −5 degrees when yaw is at 135degrees, and passing through 0 degrees when the yaw is at 0 degrees, 90degrees, and 180 degrees. The yaw and pitch angles presented above areintended only to illustrate the motion of the X-ray emitter 102 andX-ray detector 104, and are not intended to limit the disclosure to anyspecific angular motions.

Referring now also to FIG. 4, the complex curvilinear path 412 of anX-ray emitter 102 and X-ray detector 104 following the complex scanningmotion of FIG. 3 is presented. Advantageously, after all of theprojections 406 have contributed to the Fourier spectrum, there is noarea of the spectrum which is not defined. The complex scanning motiontherefore advantageously improves the spatial resolution of theresulting cone beam 3D image.

FIGS. 5A and 5B depict example embodiments of robotic scanning systems500, 520 that can be configured to perform the complex scanning motiondescribed above with regard to FIGS. 3 and 4. FIG. 5A illustrates atwo-arm robotic scanning system 500 whereby a first robotic arm 502controls the movement of the X-ray emitter 102 and a second robotic arm504 controls the movement of the X-ray detector 104. The first roboticarm 502 and the second robotic arm 504 coordinate the movements of theX-ray emitter 102 and the X-ray detector 104 to follow the complexcurvilinear path 512 when scanning an object 506.

FIG. 5B illustrates a single-arm robotic scanning system 520. A roboticarm 502 articulates and moves a C-Arm 514 capable of rotating in a firstangular direction 508 and a second angular direction 510. The roboticarm 502 and rotatable C-Arm 514 permit the single-arm robotic scanningsystem 520 to track a desired curvilinear path through a full 360-degreearc about the object and correctly position the X-ray emitter 102 andthe X-ray detector 104 relative to the object to be scanned.

In a first embodiment, the motion of the robotic scanning systems 500,520 can be captured, for example using suitable motion tracking systems,and converted into projective transformation matrices described abovefor performing the CT reconstruction.

In a second embodiment, markers (e.g., fiducials or high-density beads)associated with an object to be scanned can be used to determine themotion of the robotic scanning systems 500, 520. Motion of the objectbeing scanned can also be determined. Marker coordinates <U,V> withinthe X-ray detector 504 plane can be algorithmically detected. Thedetected <U,V> coordinates can then be used to calculate the projectivetransformation matrices.

The robotic scanning system 500, 520 first scans an object to produce anX-ray intensity image 600 of the object being scanned 602 and themarkers 604 as illustrated in FIG. 6. The X-ray intensity image 600 ofFIG. 6 is converted into a logged attenuation representation 700 asillustrated in FIG. 7. A non-linear two-dimensional high-pass filterenhances the markers 800 that permits software to determine thepositions of the markers to calculate the projective transformationmatrices.

An embodiment of a non-linear two-dimensional high-pass filter can bedefined as follows. A circle with radius R around a point <U₀,V₀> withinthe X-ray detector plane defines a set of pixels, Ω, on the X-raydetector plane. The set Ω consists of the points located at distance Rfrom pixel <U₀,V₀> as defined by the equation:

<U,V>∈Ω|√{square root over ((U ₀ −U)²+(V ₀ −V)²)}−R<1

The points Ω can be represented as the list with elements <U,V,S> whereS is the value of the image at point <U,V>. The median signal S_(M) canbe defined as:

$S_{M} = {{S_{UV}{{{\sum\limits_{i❘{S_{UV} < S_{M}}}1} - {\sum\limits_{i❘{S_{UV} \geq S_{M}}}1}}}} \leq 1}$

Assuming S_((M,U0,V0,R0)) is a median signal corresponding to the point<U₀,V₀> and radius R₀, and assuming that S_(M,U0,V0,R1)) is a mediansignal corresponding to the point <U₀,V₀> and radius R₁. Then theresponse of the nonlinear filter at the point <U,V> is:

$R_{UV} = {\max\limits_{{R_{0} < A},{R_{1} < A}}\mspace{14mu}{{S_{({M,U,V,{R\; 0}})} - S_{({M,U,V,{R\; 1}})}}}}$

where A is the filter aperture. By setting appropriate thresholds, a setof marker coordinates can be obtained algorithmically from the filteredimage, for example as depicted in FIG. 8.

An embodiment of an algorithm for calculating projection transformationmatrices from a set of projected marker coordinates is presented below.Applying the non-linear two-dimensional high-pass filter above producesa set of marker shadows <U^(n) _(i), V^(n) _(i)>, where index ncorresponds to a frame number and index i corresponds to a marker numberwithin a frame. Assuming that the system motion is “smooth”, for examplethe X-ray source and X-ray detector follow a curvilinear path during thescan, and neither the object nor the X-ray source and detector make“sharp” (highly accelerated/decelerated) moves, then any element A^(n)_(ij) of projection transformation matrix at the system angular positionn (=frame number) can be represented as:

A _(ij) ^(n) =S _(ij) ^(T)(n)

Where S_(ij) ^(T) is a spline interpolation of matrix element A_(ij). Tas a superscript indicates that a spline has T knots. This equation canbe rewritten as:

S _(ij) ^(T) =S(K _(ij) ⁰ ,K _(ij) ¹ , . . . ,K _(ij) ^(T))

Every marker has coordinates in the object space <X_(m), X_(m), Z_(m)>where m=0, . . . M−1. This provides a highly redundant system ofnonlinear equations:

U _(m)*(A ₂₀ *X _(m) A ₂₁ *Y _(m) +A ₂₂ *Z _(m) +A ₂₃)−A ₀₀ *X _(m) +A₀₁ *Y _(m) +A ₀₂ *Z _(m) +A ₀₃=0

V _(m)*(A ₂₀ *X _(m) A ₂₁ *Y _(m) +A ₂₂ *Z _(m) +A ₂₃)−A ₁₀ *X _(m) +A₁₁ *Y _(m) +A ₁₂ *Z _(m) +A ₁₃=0

where U_(m), V_(m) are known and X_(m), X_(m), Z_(m), A_(ij) areunknown.

Thus, a full system (source, detector, object) motion can be defined anddescribed by a relatively small number of factors: 11 matrixcoefficients based on (containing) T knots. In an example system, ifthere are 500 projections, 20 markers, and 12 knots as spline complexityfactors, then the system will contain [2*20*500=20000] equations with[2*20*500=20000] known values and [11*20+20*3=280] unknown values. Thehigh redundancy of the system allows the system designer to employ knownalgorithms and methods to resolve these equations with high level ofaccuracy and robustness even if the known data U_(m), V_(m) contain asubstantial portion of corrupted measurements.

Referring now to FIG. 9A, a two-arm CT core sample scanning system 900is presented. The system 900 includes an X-ray emitter 902 coupled to afirst robotic arm 912, and an X-ray detector 904 coupled to a secondrobotic arm 914. Each of the robotic arms 912, 914 can articulate androtate with six degrees of freedom, allowing movement of the X-rayemitter 902 and X-ray detector 904 in the x, y, and z directions as wellas rotation about three perpendicular axes that is commonly referred toas pitch, yaw, and roll. The robotic arms 912, 914 can be configured ina master-slave mode as would be understood in the art. In thisconfiguration, one of the robotic arms 912, 914 is the master roboticarm and synchronizes movements of both the master and slave roboticarms. Communications between the robotic arms 912, 914 can includeserial communications or Ethernet based communications among othersuitable communication protocols.

In the embodiment illustrated in FIG. 9A, the first robotic arm 912 andthe second robotic arm 914 are each secured to a respective fixed base916. In alternative embodiments, tracks or other means for moving therobotic arms 912, 914 can be substituted for the fixed bases 916 tofacilitate movement between core samples 906 and permit the system 900to monitor larger numbers of core samples 906. For example, asillustrated in FIG. 9B, a single-arm CT core sample scanning system 920has a single robotic arm 924 that is configured with a C-arm 928 havingboth an X-ray emitter 902 and an X-ray detector 904. A movable base 926is positioned on a rail system or track 922 that, using suitablecontrollers, allows the single robotic arm 924 to be repositioned alongthe track 922 in proximity to a core sample 906 to be scanned.

Example robotic arms 912, 914 include the 4600 series from ABB whichallow repeatable repositioning to within approximately 5 microns,allowing images in subsequent scans to be within about 20 microns ofprevious scans. The 4600 series robotic arms 912, 914 allow forprecision scanning of 1.5 to 6 inch cores using X-ray emitters 902capable of several hundred watts of continuous power. The type ofrobotic arms 912, 914 that can be used depends on the requiredpositioning resolution of the robotic arms 912, 914, the size and weightof the X-ray emitter 902 and X-ray detector 904, and the size of thecore sample 906 to be scanned. For example, for inch or half-inch cores,micro-CT scanners having low power CT tubes can be used which allow forsmaller robotic arms. Micro CT scanners can often achieve 12-micronresolutions or better. Future robotic arms 912, 914 may be able toprovide repeatable positioning and image down to 1-2 microns or better.In still other embodiments, the robotic arms 912, 914 can berepositioned with a precision of approximately 1/10 mm, permittingimages in subsequent scans to be within approximately ¼ mm.

A plurality of core samples 906 can be monitored by the system 900 andare positioned between the robotic arms 912, 914. The core samples arespaced apart from one another to allow the robotic arms 912, 914 to movebetween and scan each of the core samples 906. Each of the core samples906 is secured inside a metal sleeve and secured to a base 908. Hightemperature, high pressure lines 910 can be attached to the top (shown)and bottom (not shown) of the core samples 906 to assist in determiningthe properties of material in the core samples 906 for example capillarypressure, density, and immiscibility, as previously described Soaps,alcohols, or liquid CO₂ can be introduced through the lines 910 toassist in determining how best to extract substances from the groundassociated with the core samples 906. During experiments, which can berun over a period of days or weeks, the core samples 906 can beperiodically scanned by the system 900 as describe in greater detailbelow with regard to FIGS. 10-13. Advantageously, CT scanning of thecore samples 906 allows for repeated, non-invasive and non-destructiveanalysis of each of the core samples 906.

Referring now also to FIG. 10, illustrate are example robotic armpositions during a scan 1000 of a core sample 906 for a two-arm CT coresample scanning system. To begin scanning the selected core sample 906,the first robotic arm 912 positions the X-ray emitter 902 on one side ofthe core sample 906 and the second robotic arm 914 positions the X-raydetector 904 on the other side of the core sample 906. The X-ray emitter902 is turned on to emit a cone beam 1002 and the X-ray detector 904detects X-ray emissions through the core sample 906. The relativepositions of the X-ray emitter 902 and X-ray detector 904 are describedin addition detail with regard to FIG. 12 below.

Referring also to FIG. 11, the robotic arms 912, 914 move the X-rayemitter 902 and the X-ray detector 904 in complementary orbits aroundthe core sample 906 during a scan 1100 to generate additional surfacesor 2-dimensional views used in image reconstruction. The orbital pathsmove the X-ray emitter 902 and X-ray detector 904 through arcs ofapproximately 220 degrees or more, allowing the core sample 906 to beimaged sufficiently for CT reconstruction. The complementary orbits aredescribed in additional detail with regard to FIG. 12 below. Thecombined arm range 1102 of the robotic arms 912, 914 approximates acylinder around the core sample 906. Adjacent core samples 1104 arepositioned such that the robotic arms 912 will not hit the adjacent coresamples 1104 during scanning of the core sample.

FIG. 12 illustrates the relative positions and orbital paths of theX-ray emitter 902 and X-ray detector 904 during a scan 1200 of the coresample 906. To maximize resolution of the CT reconstruction, the X-rayemitter 902 and X-ray detector 904 are positioned such that the CT scancone 1002 causes all or most of the X-ray detector 904 to be used. Thisis the magnification level which is defined as SID/SOD, which is thesource image distance (SID) between the X-ray emitter 902 and the X-raydetector 904 divided by the source object distance (SOD) between theX-ray emitter 902 and the object as illustrated in FIG. 12. Depending onthe magnification, the distance from the X-ray detector 904 to the coresample 906, may be different than the distance from the X-ray detector904 to the core sample 906. Therefore, the emitter orbital path 1202 canbe different from the detector orbital path 1204 as illustrated, howeverthe emitter orbital path 1202 and detector orbital path 1204 will becomplementary to one another. Generally, the magnification level is keptconstant during scans, however the use of separate robotic arms 912, 914permits variable magnification or dynamic magnification. In anembodiment, a single robotic arm configured with an adjustable C-arm cansimilarly be used for CT scans and also achieve variable magnification.

Accommodating core samples in traditional CT scanning apparatusespresents logistical challenges. Core samples are generally very heavy,making it difficult to move core samples into position for scanning by atraditional CT scanner. Further complicating movement of the coresamples is accommodating the high temperature, high pressure lines thatare typically present during testing. Moreover, cores are typicallymounted inside of a metal sleeve, often with a rubber liner which canallow the cores to move when repositioned. Advantageously, by moving therobotic arms 912, 914 instead of the core samples 906, the material inthe core samples 906 is less likely to move, allowing subsequent scansof the core samples 906 to align with previous scans, which facilitateanalysis of changes in the core samples 906 as a result of experimentsrun on the core samples 906. However, it is possible for core samples906 to shift over time, and to precisely align scans the robotic arms912, 914 may need to take slightly different orbital paths in subsequentscans from the initial scan. While robotic arms are generally uniformlyrepositioned, there still may be some variation in relative positionsbetween a core and scanning apparatus for a stationery core. Softwarecorrection is suitably implemented to compensate for variations betweena core and scanner. This is suitably accomplished by use of a known coresample feature of either the core itself or a feature or making on thecore casing. Compensation may be in the form of modified scanningapparatus movement as noted above, or algorithmic compensation oncaptured imaging.

Referring now to FIGS. 13A and 13B, positions of the same core sample906, 906′ during an initial scan 1300 and a subsequent scan 1310 areillustrated. In the initial scan 1300 of FIG. 13A, the core sample 906has a first alignment, illustrated here as vertical only for purposes ofexplaining a concept of the disclosure. During the initial scan 1300,the X-ray emitter 902 and X-ray detector 904 are moved in theirrespective orbital paths 1302 at a plurality of vertical heights overthe length of the core sample 906. In a subsequent scan 1310 illustratedin FIG. 13B, the core sample 906′ has changed position slightly, forexample by tilting slightly at angle θ as illustrated. The controller(not shown) recalculates the orbital paths 1304 and pitch, yaw, and rollof the X-ray emitter 902 and X-ray detector 904 in order to maintain thesame spatial positioning of the X-ray emitter 902 and X-ray detector 904relative to the core sample 906′ in the subsequent scan 1310 as in theinitial scan 1300 of the core sample 906.

In order determine the position of the core sample 906, 906′ for each ofthe scans 1300, 1310 the controller performs multiple scans one or morescout scans using a reduced number of projections followed by a fullproduction scan. Whereas a production scan is a precise scan that maytake 20 minutes or more to complete, each scout scan may take just aminute or more as the scout scans are used primarily to determine theposition and alignment of the core sample 906, 906′. Once the scoutscans are complete, the controller calculates the precise adjustments tothe orbital paths 1302, 1304 necessary for the full production scan andthe full production scan is executed by the controller.

In an embodiment, the sleeve of the core sample 906, 906′ can includefeatures that assist with the scout scans as would be understood in theart, such as marks, indentations, scoring, fiducials, high densitybeads, and so forth. For example, these features can provide markercoordinates within the X-ray detector plane that can be algorithmicallydetected. The detected coordinates can then be used to calculate theposition and alignment of the core sample 906, 906′. The X-ray intensityimage in the scout scan can be converted into a logged attenuationrepresentation. A non-linear two-dimensional high-pass filter canenhance the features and permit the controller to determine thepositions of the features to calculate the position and alignment of thecore sample 906, 906′.

FIG. 14 illustrated example operations 1400 of a CT core sample scanningsystem. Operation commences at start block 1402 and proceeds to block1404 where the robotic arms are sent to their home positions, forexample as illustrated in FIG. 9. At block 1406, the scan parameters forthe robotic arms are received by the master robotic arm. For example, auser at an associated workstation may issue a set of commands through agraphical user interface or GUI to for the robotic arms to commencescanning of one of the core samples. At block 1408, the master roboticarm calculates the trajectories for the both the master robotic arm andthe slave robotic arm. At block 1410, the master robotic arm sendscommands to the slave robotic arm to synchronize the operations of bothrobotic arms to perform a linear scout scan. The linear scout scanprovides positioning information about the x, y coordinate positions ofthe core sample under test. At block 1412 the robotic arms can pause toallow the user to optionally provide z coordinate coverage for the 3Dscout scan, and at block 1414 the master robotic arm sends commands tothe slave robotic arm to synchronize the operations of both robotic armsto perform the 3D scout scan. The 3D scout scan provides informationabout the x, y, z and axis of rotation of the core sample under test. Atblock 1416 the robotic arms return to home and at block 1418 the masterrobotic arm calculates corrections for the position and axis of rotationof the core sample. Once the master robotic arm calculates thecorrections, at block 1420 the master robotic arm sends commands to theslave robotic arm to synchronize the operations of both robotic arms toperform the full production scan. Captured images from the fullproduction scan can be stored in a suitable data store such as database1422 for performing the CT reconstruction. After the full productionscan, processing returns to block 1404 where the robotic arms return tothe home position.

The foregoing description of embodiments and examples has been presentedfor purposes of description. It is not intended to be exhaustive orlimiting to the forms described. Numerous modifications are possible inlight of the above teachings. Some of those modifications have beendiscussed and others will be understood by those skilled in the art. Theembodiments were chosen and described for illustration of variousembodiments. The scope is, of course, not limited to the examples orembodiments set forth herein but can be employed in any number ofapplications and equivalent articles by those of ordinary skill in theart. Rather it is hereby intended the scope be defined by the claimsappended hereto.

What is claimed is:
 1. A method of performing X-ray computed tomography,comprising: performing a scout scan of a subject including scanning thesubject with an X-ray emitter, and capturing a first plurality of2-dimensional views by an X-ray detector; determining a starting pointfor a full production scan of the subject based at least on the scoutscan; performing a full production scan of the subject includingscanning the subject with the X-ray emitter based at least in part onthe determined starting point, and capturing a second plurality of2-dimensional views by the X-ray detector; generating a projectiontransformation matrix associated with each of the second plurality ofcaptured 2-dimensional views; applying each generated projectiontransformation matrix to data associated with each of the secondplurality of captured 2-dimensional views; and reconstructing a digitalrepresentation of the subject from the data after application of eachprojection transformation matrix, wherein the captured second pluralityof 2-dimensional views are substantially greater in number than thecaptured first plurality of 2-dimensional views.
 2. A system,comprising: a robotic arm configured to rotate an X-ray emitter in acurvilinear path about a subject while the X-ray emitter scans thesubject; an X-ray detector configured to capture a plurality of2-dimensional views while the subject is scanned by the X-ray emitter;and a computed tomography reconstruction processor configured toreconstruct a digital image of the subject from the captured pluralityof 2-dimensional views, wherein movement of the X-ray emitter and theX-ray detector is coordinated such that the position and angle of theX-ray emitter relative to the X-ray detector remains substantiallyconstant while the X-ray emitter scans the subject.
 3. The system ofclaim 2, further comprising: a rotatable C-arm, disposed on the roboticarm, that includes the X-ray emitter and the X-ray detector.
 4. Thesystem of claim 2, further comprising: a second robotic arm configuredto independently rotate the X-ray detector about the subject incoordination with the robotic arm.
 5. The system of claim 2, wherein therobotic arm is further configured to vary the pitch of the X-ray emitterwhile rotating about the curvilinear path to enable the computedtomography reconstruction processor to reconstruct a high spatialresolution digital image of the subject from the captured plurality of2-dimensional views.
 6. The system of claim 5, wherein the robotic armis further configured to sinusoidally vary the pitch betweenapproximately −5 degrees to approximately 5 degrees up to approximately−10 degrees to approximately 10 degrees.
 7. The system of claim 2,wherein the robotic arm is further configured to move in the curvilinearpath about the subject between approximately 90 degrees and 360 degrees.8. The system of claim 2, wherein the computed tomography reconstructionprocessor is further configured to generate a projection transformationmatrix associated with each captured 2-dimensional view based at leastin part on the movement of the robotic arm, and apply each generatedprojection transformation matrix to data associated with each captured2-dimensional view to reconstruct the digital image of the subject. 9.The system of claim 2, wherein the subject is a substantially verticalcore sample suspended in a metal sleeve, and wherein the robotic arm isfurther configured to move the X-ray emitter about the core sample in aplane substantially perpendicular to the axis of the core sample duringeach scan and perform a plurality of scans of the core sample at aplurality of different heights.
 10. The system of claim 9, wherein therobotic arm is further configured to selectively position the X-rayemitter about a plurality of vertically mounted core samples suspendedin metal sleeves to perform a plurality of scans of each of the coresamples at a plurality of different heights.
 11. The system of claim 10,further comprising: one or more rails disposed proximate to theplurality of vertically mounted core samples, wherein the robotic arm isfurther configured to move along the one or more rails to position theX-ray emitter proximate to each of the plurality of vertically mountedcore samples during a scan.